Clamping devices are well known and widely used within the manufacturing industry for holding different kinds of tools for machining of work pieces of various materials. The clamping device may optionally be carried on a rotatable spindle, for holding e.g. a drill or a milling tool, or be unrotatable for holding e.g. a lathe tool.
One advantage with a clamping device of this kind is that it allows for a quick clamping of the tool, simply by rotating the cam shaft by about 100° to 200°, which has the effect that the tool will be dawn by a large force into the mounting bore of the housing and thereby be securely held by the clamping device. Also, release of the tool can be easily and rapidly performed by rotating the cam shaft in the reverse direction. Normally, the bore of the housing, as well as the tool holder shank are also made slightly conical, such that they are tapered in an axial direction rearward from the tool. In this way the connection between the tool and the clamping device can be made totally free from any play, which has the effect that the tool will be held in an exact position, which allows for high precision machining by means of the tool.
However, one disadvantage with prior art clamping devices of this kind is that the drawbar is made with a comparatively large cross-sectional dimension, such that it cannot, with the desirable cross-sectional measure of the tool holder shanks frequently being used, be inserted through the bore of the housing from its forward end.
A reason why the drawbar has to be made with such a large cross-sectional dimension is that the drawbar aperture has to accommodate a cam shaft having a cam formation of a sufficient size in order to provide the desired displacement of the cam shaft and the desired force reduction for the operator performing the rotation of the cam shaft during clamping and releasing. However, in order to ensure sufficient tensile strength of the drawbar to withstand the desirable forces by which the tool holder shank is drawn into the shank bore, the remaining leg portions of the drawbar surrounding the drawbar aperture must be made with a sufficient cross-sectional dimension.
An example of a prior art design of a clamping device will be described more in detail in connection with the hereinafter detailed description of the present disclosure. Accordingly, in order to position the drawbar in place when assembling the clamping device, the drawbar has up to the present been inserted from the rear end of the clamping device or a shank bore sleeve has been mounted in the forward end of the clamping device after the drawbar has been inserted into the housing from the forward end. One consequence of this is that the overall dimensions of the clamping device cannot be made as small and slim as desired. Another consequence is that the clamping device will comprise extra mounting details, which will render the clamping device more expensive to manufacture, both in respect of material costs and costs for performing the assembling.
A prior art clamping device is described by reference to FIGS. 1-3. This prior art clamping device is of an unrotatable kind, which is adapted to hold e.g. a lathe tool. As evident from FIG. 1 an outer housing of the clamping device 1 is generally box-shaped and is shown connected to a schematically illustrated tool holder 2.
FIG. 2 is an exploded perspective view of the clamping device and the tool holder showing all the separate components comprised in the clamping device. One of the components is a drawbar 3 being inserted into the housing in a bore 4. The drawbar 3 regulates the clamping mechanism (the function of which is not further described herein) between a locked stage, in which the tool holder is firmly coupled to the clamping mechanism, and a released stage in which the tool holder is released from the clamping device.
The regulating of the clamping mechanism is performed by displacement of the drawbar 3 in the axial direction of the bore 4 in the housing. The displacement of the drawbar is in its turn performed by rotating a cam shaft 5, which extend through the housing and through an aperture in the drawbar, and which is provided with a cam formation which as desired can act on a rear surface of the aperture through the drawbar, which will displace the drawbar rearward, or on a forward surface of the aperture, which accordingly will displace the drawbar forward.
However, due to the cam formation being a locking cam surface as well as a releasing cam surface, the cam shaft will have a rather large cross-sectional dimension and accordingly, the aperture of the drawbar has to be formed with a correspondingly large cross-sectional dimension in order to accommodate the cam shaft with its cam formation. As a result, the drawbar will be formed with rather large cross-sectional dimensions, since the leg portions, which connect the forward and rear portions of the drawbar and are situated on a respective side of the drawbar aperture, also must have a certain cross-sectional dimension in order to withstand the forces that will occur.
This has the effect that with the commonly used dimensions of the mounting shanks for tools and tool holders, the drawbar cannot be inserted from the forward end of the clamping device since the passage will be too small. In the herein disclosed prior art clamping device this problem has been solved by mounting a separate sleeve 6 within the bore 4 of the housing which will define the shank bore for the mounting shank of the tool holder. Accordingly, the drawbar is mounted into the housing prior to mounting the shank bore sleeve 6.
One problem with such a solution is that the costs for manufacturing the clamping device will increase. Another problem is that using a separate shank bore sleeve will introduce one further component having its own manufacturing tolerances, which will deteriorate the precision of the machining work performed by means of the tool.